1. Field
The invention relates to pump and valve units used in supplying and controlling flow of hydraulic fluid to a hydraulically activated system. In particular the invention relates to a pump and valve unit suitable for controlling forward and reverse flows of hydraulic fluid to and from a hydraulic cylinder such as is commonly employed in raising and lowering a truck cab from its chassis.
2. State of the Art
Various four-way valves have been proposed heretofore for use in hydraulic systems such as those used in raising and lowering the cabs of large tractor-type trucks. As disclosed in U.S. Pat. Nos. 3,430,653 and 3,610,283, the valves comprise elongate, apertured valve spools rotatively mounted in valve bodies, wherein cooperative flow passages are provided in the valve spools and valve bodies for selective register by rotation of the valve spool. The valves are separate units, usually being located remote from the hydraulic pump. In U.S. Pat. No. 3,824,043, a pump and valve unit is provided wherein the pump portion and the valve portion are closely coupled in fluid flow communication by a common flow passage extending therebetween. In all of these units, especially the latter, the valve components are intricately shaped and require substantial machining.
3. Objectives
A principal objective of the present invention is to provide a compact pump and valve unit, with the pump chamber, the valve chamber, and associated flow passages being formed in a unitary body by simple machinery techniques. An additional objective is to provide a simple valve unit in which the valve spool requires minimum machining and improved sealing is achieved between the passages in the valve spool and in the valve body wherein essentially no leakage or flow loss occurs.